In addition to its essential role in nutrition, protein is an important contributor to the physical properties of formulated foods including infant formulas and foods formulated for special medical purposes. Intact proteins and partially hydrolyzed proteins contribute to the emulsification of a fat component of a nutritional product due to their favorable hydrophilic-lipophilic balance that facilitates adsorption at the interface during preparation of product. Intact proteins and partially hydrolyzed proteins also contribute to forming a strong and cohesive interfacial film that minimizes droplet coalescence in the product resulting in a stable emulsion which allows manufacture of liquid and powder nutritional products with acceptable physical properties and shelf-life.
Foods containing extensively hydrolyzed protein and/or free amino acids are frequently referred to as elemental diet products. Elemental diets contain the altered protein components to fit with special medical purposes for a selected population with suspected protein allergy, protein intolerance, malabsorption disorders, or inborn errors of metabolism. Hypoallergenic infant formulas represent an important diet alternative for babies with demonstrated protein allergy to cow's milk. In contrast to intact protein or partially hydrolyzed protein, extensively hydrolyzed protein and amino acids have very poor or negligible emulsifying properties. In the products utilizing extensively hydrolyzed protein and/or free amino acids, commercially available emulsifiers have been used to achieve acceptable physical characteristics. One such emulsifier frequently used in infant formulas and other formulated nutritional products having extensively hydrolyzed or free amino acids is an octenyl succinic anhydride modified starch (hereinafter "OSA modified starch"). It is believed that the modification of the starch contributes to emulsion stability of the formulation by reducing the boundary tension between the immiscible fluids oil and water. The OSA starch is available commercially as intact (no molecular weight reduction) or dextrinized (molecular weight reduced by heat or enzymatic treatment and the like).
When proteins, hydrolyzed proteins and/or amino acids and carbohydrates are combined in an aqueous solution, these components have a tendency, especially with time and at elevated temperatures, to form a brownish solution and undesirable by-products due to the well-known Maillard reaction(s). This problem is particularly challenging for formulas prepared with extensively hydrolyzed proteins and/or free amino acids. U.S. Pat. No. 4,414,238 (Schmidl) teaches an elemental diet composition that uses an OSA modified starch in combination with a mono- and diglycerides emulsifier at a pH range of from about 3 to 4.4 to provide acceptable emulsification stability in conjunction to reduce the Maillard reaction. The pH range is attributed to providing an aqueous combination that is non-browning with time and at elevated temperatures and can be pasteurized or sterilized without the formation of Maillard reaction related by-products or undesirable browning.
U.S. Pat. No. 4,670,268 (Mahmoud) teaches that an OSA modified starch may be used in formulations with extensively hydrolyzed proteins at a higher pH of from 6 to 7. This patent also teaches that mono- and diglycerides, lecithin and polyglycerol esters of fatty acids were found to be ineffective in producing a stable hypoallergenic formula. As provided in Col. 4, lines 13-16 of U.S. Pat. No. 4,670,268, the hypoallergenic formula made with these emulsifiers yielded unstable emulsions and developed an objectionable cream layer within 24 hours of sterilization.
The OSA modified starch has been found incompatible with simple emulsifiers, as discussed in the prior art literature and exemplified in the Examples section herein. Thus, in commercially available nutritional products with extensively hydrolyzed proteins, dextrinized OSA modified starch is often used as a sole emulsifier in elemental diet compositions (see, e.g., U.S. Pat. No. 4,670,268).
While products with extensively hydrolyzed proteins and/or amino acids are commercially available, alternative emulsifying systems for elemental diets are needed.